Some of the factors that cause loss of freshness of a vegetable, which is an example of produce, are temperature, humidity, environmental gas, microorganisms, and light. Respiration and transpiration of vegetables continue even after harvest. To preserve freshness of vegetables, respiration and transpiration need to be suppressed. In many vegetables, except some which are susceptible to low temperature damage or the like, the respiration is suppressed in low temperature and the transpiration can be prevented by high humidity.
In recent years, to preserve freshness of vegetables, some of household refrigerators include a sealed vegetable container and are controlled such that vegetables are cooled to a proper temperature and humidity in the vegetable container is increased to suppress transpiration by the vegetables. Furthermore, some refrigerators employ a mist spray unit to achieve high humidity in the vegetable container.
Conventionally, this type of refrigerator having a mist spray function generates and sprays a mist by vibrating a hygroscopic material using an ultrasonic oscillator. With the mist, inside of a vegetable compartment is humidified to suppress the transpiration by vegetables (for example, see Patent Literature (PTL) 1).
FIG. 6 and FIG. 7 show the conventional refrigerator described in PTL 1.
As shown in FIG. 6, the refrigerator includes a vegetable compartment 4 that is of a drawer type. A refrigerator compartment 2 and the vegetable compartment 4 are partitioned by a partition plate 8. The partition plate 8 includes a hole 9 that is for allowing cool air to flow into the vegetable compartment 4 from the refrigerator compartment 2. To the vegetable compartment 4, a vegetable container 10 is provided. The vegetable container 10 moves with the vegetable compartment 4. Furthermore, disposed on the top part of the vegetable container 10 is a vegetable container lid 11 that closes the vegetable container 10 in a state where the vegetable compartment 4 is pushed in. The vegetable container lid 11 includes an ultrasonic humidification unit 12 with which water is sprayed into the vegetable container 10.
Furthermore, as shown in FIG. 7, the ultrasonic humidification unit 12 is provided in a hole 15 of the vegetable container lid 11 and includes an water absorbent material 16 and an ultrasonic oscillator 17.
The following describes an operation of the refrigerator having the above-described structure.
When the temperatures in the refrigerator compartment 2 and the vegetable compartment 4 gets high, a refrigerant is provided to a cooler 13 and a fan 14 is driven. As a result, as indicated by arrows in FIG. 6, cool air around the cooler 13 flows through the refrigerator compartment 2, the hole 9, and the vegetable compartment 4 and then returns to the cooler 13. Thus, the refrigerator compartment 2 and the vegetable compartment 4 are cooled. This state is referred to as a cooling mode.
Then, when the cooling of the refrigerator compartment 2 and the vegetable compartment 4 is almost achieved, supply of the refrigerant to the cooler 13 is stopped. However, the fan 14 continues to operate. With this, frost adhering to the cooler 13 melts, and the refrigerator compartment 2 and the vegetable compartment 4 are humidified. This state is referred to as a humidification mode (the so-called “moisture operation”).
After the humidification mode is continued for a predetermined time period (several minutes), the fan 14 is stopped to switch to an operation stop mode.
Subsequently, when the temperature in the refrigerator compartment 2 and the vegetable compartment 4 gets high, the refrigerator enters the cooling mode again.
The following describes the ultrasonic humidification unit 12.
The water absorbent material 16 is made of a water-absorbing material such as silica gel, zeolite, and activated carbon. Thus, during the above-mentioned humidification mode, the water absorbent material 16 adsorbs water contained in the flowing air. Then, the ultrasonic oscillator 17 is driven in the latter part of the cooling mode. This causes the water in the water absorbent material 16 to be discharged to the outside. With this, inside of the vegetable container 10 is humidified. Note that the driving of the ultrasonic oscillator 17 in the latter part of the cooling mode is intended to prevent the drying of stored items caused by a decrease in humidity in the vegetable compartment 4.